1. Field of the Invention
The present invention relates to a data processing apparatus capable of reducing the burden on a control unit associated with encryption and decryption of stored data.
2. Description of Related Art
In recent years, integration of functions has been advanced for an image processing apparatus which is provided with a copying function for scanning an original image and copying the image. An image processing apparatus provided with a plurality of functions has been put to practical use by adding, to a copying function, a network printer function for receiving image data from an outer device such as a personal computer (PC) and outputting an image when the apparatus is connected with a communication network such as the LAN, and a facsimile function for transmitting and receiving image data to and from an outer facsimile machine using a facsimile communication and the like. Such an image processing apparatus comprises storing means, such as a hard disk or a semiconductor memory, for temporarily storing image data to be processed. An image processing apparatus can process a plurality of image data effectively without causing stagnation by storing inputted image data in sequence in storing means and processing image data stored in the storing means when its turn for processing comes.
Some image data to be processed by an image processing apparatus in a copying operation of an original image or in an output operation of an image includes confidential information such as a document with personal information or trade secret. When image data including confidential information is stored in storing means of an image processing apparatus, information is at risk for being leaked by unjust fetch of image data stored in the storing means. A technique has been therefore developed for preventing unjust fetch of image data stored in storing means and leakage of information, by storing image data in an encrypted form in storing means and processing the image data after decrypting the encrypted image data (see, for example, Japanese Patent Application Laid-Open No. S64-64173 (1989)).
In addition to image data itself, data to be processed by an image processing apparatus further includes other data such as a processing instruction of image data or a control instruction of storing means. Since it is needless to encrypt these data other than image data, it is required to discriminate data which is to be encrypted from data which is not to be encrypted. A conventional image processing apparatus comprises a control unit constructed with a CPU, a RAM and the like, and the control unit controls various functions of the image processing apparatus such as a copying function, a facsimile function and storing means and discriminates data to process encryption and decryption of image data. Consequently, an image processing apparatus for processing encryption and decryption of image data has a problem that the burden on the control unit is large. Especially, when the image processing apparatus deals a color image, the burden on the control unit is significantly increased since color image data has a volume extremely larger than monochrome image data. Consequently, there is a problem that the processing efficiency and the processing speed of an image processing apparatus are lowered as the burden on the control unit is increased. There is another problem that the cost of an image processing apparatus rises when a high-performance control unit is used to avoid lowering of the processing efficiency and the processing speed of an image processing apparatus.